Polycrystalline diamond (PCD) has been widely used as wear and/or cutting elements in industrial applications, such as for drilling subterranean formations and metal machining for many years. Typically, such PCD cutting elements are provided in the form of a compact that comprises a body formed from PCD (or other super hard material), and that is attached to substrate material, which is typically a sintered metal-carbide to form a cutting structure. Such compact body comprises a polycrystalline mass of diamonds (typically synthetic) that are bonded together to form an integral, tough, high-strength mass or lattice. In such conventional PCD, the body is formed of a uniform or homogeneous distribution of diamond bonded crystals. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.
Conventional PCD compacts can be formed by placing a cemented carbide substrate into a container of a press. A desired mixture of diamond grains, or diamond grains and catalyst binder, is placed adjacent the substrate and treated under high pressure, high temperature (HPHT) conditions. In doing so, the metal binder material present in the substrate (often cobalt) infiltrates from the substrate and passes through the diamond grains to promote intercrystalline bonding between the diamond grains. As a result, the diamond grains become bonded to each other to form the PCD body, and the PCD body is in turn bonded to the substrate. The substrate often comprises a metal-carbide composite material, such as tungsten carbide. The so formed PCD body is often referred to as the “diamond table” or “abrasive layer” of the compact or cutting element structure.
Conventional PCD includes in the range of from about 85-95% by volume diamond and a balance binder or catalyst material, which binder or catalyst material is present in the PCD microstructure within interstitial regions existing between the bonded together diamond grains. Binder or catalyst materials that are typically used in forming PCD include metal solvent materials selected from Group VIII of the Periodic table, with cobalt (Co) being the most common. Further, such conventional PCD comprises a material microstructure made of a substantially uniform phase of bonded together diamond crystals, with the binder or catalyst material disposed within interstitial regions that exist between the bonded diamond crystals.
A problem known to exist with conventional PCD construction, i.e., those comprising a uniform or homogeneous microstructure of bonded together diamond grains is that when used as a cutting element on a drill bit, the rate of penetration (ROP) or speed in which the drill bit progresses through such hard formations may often be reduced, or slowed. This is believed due to the fact that the homogeneous structure of the PCD cutting element is unable to provide cutting surfaces or edges that will optimally engage and remove formation material. Further, conventional PCD having such a homogeneous diamond bonded microstructure, having homogeneous wear characteristics, may allow an initially sharp cutting edge to become rounded with use. Such rounding or dulling of the cutting edge also reduces the ability and effectiveness of the cutting element to remove the formation material
A further problem known to exist with such conventional PCD materials is that they are vulnerable to thermal degradation, when exposed to elevated temperature cutting and/or wear applications, caused by the differential that exists between the thermal expansion characteristics of the interstitial catalyst material and the thermal expansion characteristics of the intercrystalline bonded diamond. Such differential thermal expansion is known to occur at temperatures of about 400° C., can cause ruptures to occur in the diamond-to-diamond bonding, and eventually result in the formation of cracks and chips in the PCD structure, rendering the PCD structure unsuited for further use.
Another form of thermal degradation known to exist with conventional PCD materials is one that is also related to the presence of the metal catalyst in the interstitial regions and the adherence of the solvent metal catalyst to the diamond crystals. Specifically, the solvent metal catalyst is known to cause an undesired catalyzed phase transformation in diamond (converting it to carbon monoxide, carbon dioxide, or graphite) with increasing temperature, thereby limiting practical use of the PCD material to about 750° C.
Attempts at addressing such unwanted forms of thermal degradation in conventional PCD materials are known in the art. Generally, these attempts have focused on the formation of a PCD body having an improved degree of thermal stability when compared to the conventional PCD materials discussed above. One such known technique of producing a PCD body having improved thermal stability involves, after forming the PCD body, removing all or a portion of the solvent catalyst material therefrom.
For example, U.S. Pat. No. 6,544,308 discloses a PCD element having improved wear resistance comprising a diamond matrix body that is integrally bonded to a metallic substrate. While the diamond matrix body is formed using a catalyzing material during high temperature/high pressure processing, the diamond matrix body is subsequently treated to render a region extending from a working surface to a depth of at least about 0.1 mm substantially free of the catalyzing material.
Other references disclose the practice of removing substantially all of the catalyst material from the PCD body, thereby forming so-called thermally stable polycrystalline diamond or TSP. While this approach produces an entire PCD body that is substantially free of the solvent catalyst material, is it fairly time consuming. Additionally, a problem known to exist with this approach is that the lack of solvent metal catalyst within the PCD body precludes the subsequent attachment of a metallic substrate to the PCD body by solvent catalyst infiltration.
Additionally, such TSP materials have a coefficient of thermal expansion that is sufficiently different from that of conventional substrate materials (such as WC-Co and the like) that are typically infiltrated or otherwise attached to the PCD body. The attachment of such substrates to the PCD body is highly desired to provide a PCD compact that can be readily adapted for use in many desirable applications. However, the difference in thermal expansion between the TSP body and the substrate, and the poor wetability of the TSP body diamond surface due to the substantial absence of solvent metal catalyst, makes it very difficult to bond TSP to conventionally used substrates. Accordingly, such TSP bodies must be attached or mounted directly to a device for use, i.e., without the presence of an adjoining substrate.
Since such TSP bodies are devoid of a metallic substrate they cannot (e.g., when configured as a cutting element for use on a bit for subterranean drilling) be attached to such drill bit by conventional brazing process. The use of such TSP bodies in this particular application necessitates that the TSP body itself be mounted to the drill bit by mechanical or interference fit during manufacturing of the drill bit, which is labor intensive, time consuming, and does not provide a most secure method of attachment.
While these above-noted known approaches provide insight into diamond bonded constructions capable of providing some improved degree of wear resistance, abrasion resistance, and/or thermal stability when compared to conventional PCD constructions, it is believed that further improvements in one or more such properties for PCD materials useful for desired cutting and wear applications can be obtained according to different approaches that are both capable of minimizing the amount of time and effort necessary to achieve the same, and that permit formation of a PCD composite having improved such one or more improved properties comprising a desired substrate bonded thereto to facilitate attachment of the construction with a desired application device.
It is, therefore, desired that polycrystalline diamond constructions be developed having a polycrystalline diamond body engineered to have an improved degree of thermal stability and/or wear/abrasion resistance when compared to conventional PCD materials, and that include a substrate material bonded to the polycrystalline body to facilitate attachment of the resulting construction to an application device by conventional method such as welding or brazing and the like. It is further desired that such polycrystalline diamond constructions also be capable of providing a desired degree of impact resistance and strength that is the same as or that exceeds that of conventional PCD.